I agree, that can tell you a fair bit more about their development skills, and a bit more about their interpersonal skills, but I think it only gives you so much in the latter area. The inter-personal "fit" can be one of the most important factors in the success of a hire, and you're not going to get more than a taste of that by looking at a bunch of mailing list interactions (and that may not tell you much at all about how they interact with others on a face-to-face team). Sure, having this extra info is better than not having it, but it only gets you so far.